Systems on a chip (SOC) have been implemented in a number of capacities over the last few decades. SOC solutions offer the advantage of scaling which cannot be matched by board-level component integration. While analog and digital circuits have long been integrated onto a same substrate to provide a form of SOC that provides mixed signal capabilities, SOC solutions for mobile computing platforms, such as smart phones and tablets, remain elusive because these devices typically include components which operate with two or more of high voltage, high power, and high frequency. As such, conventional mobile computing platforms typically utilize group III-V compound semiconductors, such a GaAs heterojunction bipolar transistors (HBTs), to generate sufficient power amplification at GHz carrier frequencies, and laterally diffused silicon MOS (LDMOS) technology to manage voltage conversion and power distribution (battery voltage regulation including step-up and/or step-down voltage conversion, etc.). Conventional silicon field effect transistors implementing CMOS technology is then a third device technology utilized for logic and control functions within a mobile computing platform.
The plurality of transistor technologies utilized in a mobile computing platform limits scalability of the device as a whole and is therefore a barrier to greater functionality, higher levels of integration, lower costs, and smaller form factors, etc. While an SOC solution for the mobile computing space that would integrate two or more of these three device technologies is therefore attractive, one barrier to an SOC solution is the lack of a scalable transistor technology having both sufficient speed (i.e., sufficiently high gain cutoff frequency, Ft), and sufficiently high breakdown voltage (BV).
One promising transistor technology is based on group III-nitrides (III-N). However, this transistor technology faces fundamental difficulties in scaling to feature sizes (e.g., gate length) less than 100 nm where short channel effects become difficult to control. Scaled III-N transistors with well-controlled short channel effects are therefore important to achieving high Ft/Fmax, with sufficiently high breakdown voltage (BV). For an SOC solution to deliver the product specific electrical current and power requirements of a mobile computing platform, fast switching high voltage transistors capable of handling high input voltage swings and providing high power added efficiencies at RF frequencies are needed. An advanced III-N transistor amenable to scaling and such performance is therefore advantageous.